The present invention is directed to a composition and method for reducing or preventing formation of organic residue and scum derived from photolithographic compositions from a substrate or a solution. More specifically, the present invention is directed to a composition and method for reducing or preventing the formation of organic residue and scum derived from photolithographic compositions from a substrate or a solution where the composition contains an aromatic alkoxylate in combination with a polyol.
Contaminants such as built-up organic residue and scum from photolithographic compositions present difficult cleaning problems for the electronics industry. Photolithographic residue and scum such as from photoresist developer solutions, stripper solutions and the like can build-up on various products and apparatus. Photoresist materials are employed in the manufacturing of semiconductor devices, and electronic components such as integrated circuits, photomasks for the manufacturing of integrated circuits, printed wiring boards and the like as well as planographic printing plates. In photolithographic processing, a substrate surface is coated with a photoresist, i.e., a coating composition that is sensitive to actinic radiation, e.g., ultraviolet light, X-rays, electron beams and the like, to give a layer that is sensitive to actinic radiation which is irradiated pattern-wise with the actinic radiation. The irradiated photoresist is then developed with a developer solution to form a patterned photoresist layer that serves to selectively protect the substrate surface from etching, plating or diffusion of dopants.
Photoresists may be positive-working, or negative-working. Such photoresists may be liquid, or dry film. A photoresist composition of the positive-working type has such a photosensitivity that solubility of the composition in the developer solution is increased by exposure to light so that the patterned photoresist layer is formed on the areas unexposed to ultraviolet light where the composition is left undissolved. A negative-working photoresist composition exhibits behavior of a sensitivity and solubility that is the reverse of the positive-working photoresist.
Along with recent progress in the technology of semiconductor devices with a requirement for finer and finer high-fidelity patterning of a line width of 1 micron or even finer to comply with the trend of increased density of integration in semiconductor devices, photolithographic processes of patterning using a positive-working photoresist also envisages a difficult problem. When patterning is desired of an extremely fine contact hole in a fine pattern, alkaline developer solution is admixed with a surface active agent with an object to increase the wettability of the substrate surface with the aqueous developer solution. One of the problems in the addition of a surface active agent to the developer solution, is that film residues and scums sometimes occur on the exposed areas where the photoresist layer is desirably dissolved away as completely and cleanly as possible. Although the film residues and scums can be removed by gently treating the surface with oxygen plasma or sputtering, no complete solution to the problem can be obtained by such methods because such treatments must be performed under well controlled troublesome conditions, and is not efficient in respect of smooth removal of the scums, or gives no uniform effect of treatment in finely patterned areas having contact holes of about 1 micron or smaller in diameter.
U.S. Pat. No. 4,820,621 to Tanaka et al. has addressed the problem of residue and scum formation by modifying a developer solution with the addition of a non-ionic surface active agent that is a polyoxyethylene alkyl-substituted phenyl ether. The ether is included in the developer solution in an amount of from 50 to 5000 ppm (parts per million). The developer solution is employed in patterning using a positive-working photoresist composition composed of an alkali-soluble novolac resin and a naphthoquinone diazide compound. The '621 patent alleges that patterning the positive photoresist with the developer containing the polyoxyethylene alkyl-substituted phenyl ether prevents formation of residues and scums after development.
Similar residue and scum formation also occur when negative-working photoresists are employed. For example, in manufacturing printed circuit boards UV curable negative-working photoresists may be used. Exposed portions of the photoresist become insoluble in alkaline developer solution and form a protective barrier to other processing chemicals such as etching and plating solutions. Unexposed portions of the photoresist are to rinse freely from the circuit board with an alkaline solution such as a 1% sodium carbonate, monohydrate in water. Development occurs because polymers in the photoresist contain acid functionality. Such acid functionality within the polymers are neutralized in alkaline solution forming a water soluble organic salt. As the dissolved photoresist builds up in solution (developer loading), insoluble organic materials, such as uncured photoresist, begin to form in the developing tank eventually forming a water insoluble residue or scum. Presence of anti-foam additives (conventionally added to developing solutions to minimize foaming) greatly increases the tendency for residue and scum to form. As the level of scum builds, chances increase for an inadvertent redeposit of these water insoluble residues onto the developed circuit board. Such redeposited residues cause a retardation of the etching solution (etching chemistries have difficulty penetrating any organic residues). Where etch is retarded, circuit shorts form causing a defective circuit board. In addition to increasing the potential for defective circuit boards, the residue also makes cleaning equipment difficult, thus increasing maintenance time. Such residue and scum can adhere to developer apparatus surfaces, plug nozzles, and redeposit onto surfaces of printed wiring boards causing defects in the boards.
In addition to the problem of built-up residue and scum formation from primary photoresists, there also is a residue and scum build-up problem from secondary photoresists. Such secondary photoresists may be employed in soldermasks. Residue and scum are deposited on a substrate as a result of component separation in the soldermask. Such component separation may be exacerbated when an improperly balanced soldermask developer solution, i.e., improper developing conditions and/or soldermask developer solution chemistry, contact the soldermask. Built-up residue and scum from secondary photoresists often appear as a bright green coating on a substrate such as a developer apparatus.
Cleaners used to remove residue and scum may vary in composition. Typically, cleaners include as active ingredients a strong base such as sodium hydroxide, and chelating agents such as ethylene diamine tetraacetate (EDTA). Surfactants, solvents and emulsifying agents may also be included in the cleaners. Cleaners are employed at temperature ranges from about 45° C. to about 55° C. Many cleaners are primarily used because of the low cost of their ingredients. However, workers in the field using such cleaners have discovered that the residue problem is often made worse. Often the equipment has to be manually cleaned to remove the residue from the photoresist as well as from the cleaners. Such manual cleaning is both a labor and time intensive operation that can cause a significant loss of production time. Further, many cleaners are not effective enough for removing residue and scum from new generation photoresists that have many hydrophobic aromatic materials.
U.S. Pat. No. 5,922,522 to Barr et al.; U.S. Pat. No. 6,063,550 to Lundy et al.; and U.S. Pat. No. 6,248,506 B1 to Lundy et al. disclose surfactant and surfactant mixtures added to developer solutions that prevent or inhibit the formation of residues and scum on circuit boards and circuit board manufacturing equipment. Such surfactants are composed of a hydrophobic group, an alkoxylated hydrophilic group and a nonionic or anionic capping group. Examples of suitable hydrophobic groups include nonylphenol, octylphenol and tristyrylphenol. Examples of suitable alkoxylated hydrophilic groups include ethylene oxide, propylene oxide and ethylene oxide/propylene oxide groups. Examples of suitable capping groups include hydroxyl, carboxyl, sulfonyl, phosphonyl, or mixtures thereof. Such residue and scum reducing compounds are included in developer solutions in amounts of from about 0.05% to about 1.0% by weight.
Although the developer solutions disclosed in U.S. Pat. No. 5,922,522; U.S. Pat. No. 6,063,550; and U.S. Pat. No. 6,248,506 B1 provide an effective means of reducing the amount of build-up of residue and scum on substrates containing photoresist, such as circuit boards, and equipment used in the manufacture of electronic components, there is still a need for an improved composition and method for reducing or preventing formation of residue and scum on various substrates such as developer apparatus as well as developer solutions. Regardless of the efforts to prevent build-up of residue and scum in developer apparatus, such as a conventional spin developer, or a spray developer where developer solution is sprayed onto a substrate surface, repeated use of such apparatus inevitably results in the build-up of residue and scum. At a certain point, the residues and scum accumulate to such an extent that the equipment is shut down for cleaning, thus reducing product output. Such residue and scum may include hydrophobic aromatic materials such as photoinitiators, dyes, (meth)acrylic monomers and other organic materials that make up photoresists as well as antifoam agents and surfactants. Such built-up residue and scum are often difficult to re-emulsify with many developer apparatus cleaners.
In addition to residue and scum formation, excessive foaming is another problem. When photoresist is removed from a substrate with a developer solution, foaming occurs. Excessive foaming during photoresist removal may cause developer solution levels to go below their effective minimum threshold levels. Such a condition results in developer equipment shutdown and reduced product out-put. Foaming may also obscure a workers field of view during manufacturing of printed wiring boards making it difficult to determine photoresist break points, and to monitor printed wiring board panels in developing chambers resulting in printed wiring board defects. Additionally, cleaning equipment that contains large amounts of foam is difficult. Rinsing a foam contaminated apparatus with water aggravates foam formation.
Accordingly, there is a need for a composition and method that reduces or prevents residue and scum formation from photolithographic compositions as well as reducing or preventing foam formation during development of photoresist.